A method of this kind is disclosed, for example, in U.S. Pat. No. 5,471,406. In this known method, geometric data of geometric elements of the workpiece in the form of desired data are transferred from a computer to the control system of the coordinate measuring apparatus. In the control system, the desired data are transformed into the machine coordinate system and are thereafter transferred to an interpolator which generates the position desired values along which the probe head with the movably attached probe is control driven. Furthermore, and in one embodiment, a desired measuring force is transferred additionally from the computer to the control system. A force controller continuously charges the probe with a measuring force relative to the probe head. This measuring force has a constant magnitude and is always normal to the workpiece surface to be measured.
Particular to the above method is that the magnitude of the adjusted measuring force is constant during the entire measuring sequence and corresponds to the pregiven desired measuring force. The actual probe force with which the probe ball of the probe is pressed against the surface of the workpiece to be measured, however, changes because of mass inertial forces which occur with accelerations of the probe. Centrifugal accelerations occur especially when scanning curved surface sections of the workpiece. These centrifugal accelerations act in the direction of the measuring force in concave curves so that the actual force with which the ball of the probe is pressed against the surface of the workpiece is increased. For convex curves, the centrifugal accelerations operate opposite to the measuring force and thereby reduce the actual force with which the ball of the probe is pressed against the surface of the workpiece. For a rapid movement on convex curves, the centrifugal force can even be greater than the applied measuring force so that the probe, that is, the probe ball attached thereto, lifts off of the workpiece surface. In each case, the measuring results are made incorrect by the above effects so that the path speed of the probe must be greatly reduced before reaching the curved surface sections of the workpiece to avoid the above effects. This is described in detail in U.S. patent application Ser. No. 08/693,632, filed Aug. 9, 1996, and incorporated herein by reference.
The reduction of the path speed, however, leads to increases in measuring time especially for workpieces which have many curves such as gear wheels, shafts, engine blocks, et cetera.